The Devel::SawAmpersand module only provides one function:

$bool = Devel::SawAmpersand::sawampersand();

which is set to true if perl saw any of $`, $', $& in its code.

Devel::FindAmpersand is a bit more precise.

B::FindAmpersand is supposed to scan code to look for those variables,
but it doesn't appear to be very reliable.

Due to some design decisions, regexp matching suffers from performance
issues as soon as one of these variables is used.
